The Secondary Aims are to examine the correlation between the aspirin-related changes in microbiome profile with the levels of circulating inflammatory biomarkers in urine and plasma. Within-individual and between-arm differences in microbiome composition will be compared after 3 and 6 weeks of aspirin intake. Also, the microbiome composition will be compared after 3-week and 6-week wash-out periods to test whether these periods are sufficient to restore gut microbiome composition to a pre-treatment level. This study will inform future crossover randomized studies focusing on CRC preventive interventions that will enable clinicians to identify optimal candidates for aspirin therapy for the purposes of CRC prevention using this accessible and cheap drug.